This would mark the first time Pakistan's has used these jets in combat against Indian forces, which could have major repercussions.

The Indian military has publicly displayed a portion of an AIM-120C-5 Advanced Medium-Range Air-to-Air Missile, or AMRAAM, as evidence that Pakistani F-16 Viper fighter jets were at least involved in recent strikes on the Indian-administered portion of the disputed Jammu and Kashmir region. India continues to say that it shot down one of the Vipers, which Pakistan denies, as the two nuclear-armed countries work to de-escalate a major spike in tensions and pull back from the brink of war. Regardless, this would be the first time Pakistan has used these American-made fighter jets in action against Indian forces, which could have serious ramifications for its relationship with the United States.

Indian Air Force Air Vice Marshal R.G.K. Kapoor presented the piece of the missile at a joint press conference on Feb. 28, 2019, regarding the state of the situation with Pakistan follow a series of tit-for-tat aerial engagements that left an Indian pilot in Pakistani custody. Pakistan says it plans to release Wing Commander Abhinandan Varthaman as a good will gesture on Mar. 1, 2019. The Pakistanis shot down Varthaman, who was flying a MiG-21 Bison at the time, during an aerial battle on Feb. 27, 2019, but deny F-16s were involved in any way. Other reports, citing unnanmed sources, say that a JF-17 Thunder was actually responsible for the shoot down.

“Pakistan claimed they did not use F-16. There are enough evidences through electronic signature that F-16 was used," Kapoor said at the press conference. "Parts of AMRAAM air-to-air missile, which is carried only by PAF [Pakistani Air Force] F-16, was recovered east of Rajouri within the Indian territory [in Jammu and Kashmir]."

Pakistan has a fleet of around 76 F-16, which are a mix of A/B Air Defense Fighter (ADF), AM/BM Mid-Life Update (MLU), and Block 52 C/D models. These include jets acquired directly from the United States and from second-hand sources. It has also received AIM-120C-5 missiles to go along with them. India does not use any variant of the AIM-120.

AP Photo/Manish Swarup

Indian Air Force personnel show a fragment from an AIM-120C-5 missile as evidence that Pakistani F-16s were involved in recent strikes on Indian positions during a press conference on Feb. 28, 2019.

Some claimed that the contract number shown on the missile fragment identified it as one shipped to Taiwan, suggesting the evidence was fabricated. However, this contract was actually a larger U.S. Foreign Military Sales deal that did involve deliveries to Pakistan.

Kapoor said that Indian radars had identified a large strike package consisting of Pakistani F-16s and JF-17 Thunders heading toward the Line of Control, which separates Indian and Pakistani forces in Jammu and Kashmir, on Feb. 27, 2019. The force may have also included older Mirage III or Mirage 5 aircraft. He did not say whether it was Indian radars that had identified the signature of the Vipers or if another electronic intelligence system was involved.

Indian Su-30MKI, MiG-21, and Mirage 2000 fighter jets then moved to intercept. Separate, unconfirmed reports, citing anonymous sources, say that Wing Commander Varthaman was chasing a Pakistani F-16 in his Bison and shot it down with a Russian-made R-73 heat-seeking air-to-air missile.

Sheeju via Wikimedia

An Indian MiG-21 Bison. An R-73 missile is visible on the outboard pylon of the left wing.

"Fact is that Indian Army units reported sighting two parachutes falling in PoK [Pakistani-occupied Kashmir] which were of two F-16 pilots shot down by the IAF MiG," Air Vice Marshal Kapoor, said during the press conference. If true, this would indicate that the aircraft in question was one of Pakistan's two-seat F-16B or D models. India has consistently claimed it shot down only one aircraft.

Asuspine via Wikimedia

A Pakistani F-16BM combat jet with a training version of the AIM-120 on its wingtip launch rail.

Unconfirmed reports suggest that Wing Commander Varthaman may have pressed his attack on the Pakistani F-16 beyond the safety afforded by the larger Indian force, which also left his wingman vulnerable. Another Pakistani combat jet then shot down MiG-21.

This may or may not have been another F-16. India has not made it clear they believe the fragment of the AIM-120C-5 was the result of a Viper firing it at an Indian aircraft or whether it broke off from the one Varthaman reportedly shot down.

AP Photo/Abdul Razzaq

A Pakistani soldier stands guard next to some of the wreckage of Wing Commander Abhinandan Varthaman's MiG-21 Bison.

Separate reports have suggested a Pakistani JF-17 Thunder was responsible for actually shooting down the Indian MiG-21. A video has emerged of triumphant Pakistani Air Force pilots celebrating the air-to-air victory in front of one of these jets.

If the latter is the case, it would be the first known aerial combat engagement by a Thunder, a light fighter that Pakistan developed together with China, and one that resulted in an air-to-air victory. The Pakistanis and Chinese have been marketing the aircraft heavily around the world and this combat outing could become a prominent feature in future sales materials regardless.

Shimin Gu via Wikimedia

A Pakistani Air Force JF-17.

There remains no hard evidence of the F-16 shoot down itself. Pictures have emerged online purporting to show Pakistani personnel recovering wreckage of an F110 engine, but none of Pakistan's Vipers use this engine. The images actually appear to show parts of Varthaman's MiG-21.

This is a prime example of very active the rumor mill in both India and Pakistan and how difficult it can be difficult to separate facts from the rapid-fire deluge of often misleading or outright false information online. For instance, in the aftermath of the Feb. 27, 2019, a video circulated widely across social media, making it into actual media reports, allegedly showing a second Indian pilot seriously injured after getting shot down by Pakistani aircraft. This video, however, is from an entirely unrelated accident at the 2019 Aero India airshow and exhibition involving two planes from the Surya Kiran Aerobatics Team.

Pakistan also claims that it shot down a second Indian jet, which crashed on the Indian side of the Line of Control. India denies this occurred and there has been no clear evidence, so far, to prove otherwise. An Indian Mi-17V5 helicopter did crash in Jammu and Kashmir on Feb. 27, 2019, but Pakistani authorities have not claimed to have shot down a rotorcraft and India says the mishap was due to a mechanical fault.

But even just an engagement between an Indian MiG-21 and a Pakistani F-16 would be significant in of itself. Though aging and increasingly hard to maintain, the Indian Air Force's Bisons have received significant upgrades over the years, including the ability to carry Israeli-made Elbit EL/L8222 self-escort jamming pods. The Soviet-era design also benefits from a relatively small radar cross-section and visual signiture and Indian pilots have helmet mounted sights that give them the ability to launch R-73s high-off boresight at particularly opportune times.

Indian MiG-21s and their pilots famously surprised U.S. Air Force aviators during a major air combat exercise called Cope India in the country in 2004. Working closely with other Indian combat jets, they were able to repeatedly get the drop on American fliers in F-15C Eagles.

“The MiG-21s would be embedded with a [MiG-27] Flogger for integral protection. There was a data link between the [Su-30MKI] Flankers that was used to pass information,” U.S. Air Force Colonel Greg Newbech, a participant in the 2004 drill, said in a subsequent interview. “They built a very good [radar] picture of what we were doing and were able to make good decisions about when to roll [their aircraft] in and out.”

USAF

Indian MiG-27 Floggers and US Air Force F-15C Eagles fly together during Cope India 2004.

Beyond the Bison presenting a challenge to the F-16 in a real life combat scenario, there could be serious political ramifications. An American-made plane firing an American-made missile could have political ramifications in the future as the United States drifts away from its historical relationship with Pakistan and looks to dramatically improve its ties, especially its military-to-military relationship, with India.

F-16 sales to Pakistan have been controversial since the first examples arrived in the country in the 1980s. In 1990, Congress put measures into place to halt economic and military cooperation with Pakistan over its development of nuclear weapons, which blocked further Viper deliveries for a time.

In 2005, the United States once again began approving F-16 sales to Pakistan, as well as allow the country to upgrade its existing aircraft, but with heavy export controls in place. There are reports that this includes limiting access to key systems on the jets, as well as Pakistan's ability to service those components. Rumors of tracking devices and the ability to remotely disable the aircraft, or key systems on it, have also been circulating for years.

Even so, in 2016, American legislators again held up Viper sales over Pakistan's inability or unwillingness to tackle terrorist groups within its borders, including those conducting attacks on U.S. forces and their allies in Afghanistan. With the U.S. government now in the midst of a major push to expand relations with India and increase shared military activities with its forces in South Asia and beyond, members of Congress could see the latest exchange as even more reason to block future military aid to Pakistan.

USAF

A Pakistani Air Force F-16C at Nellis Air Force Base in Nevada during a training exercise in 2016.

Since taking office, President Donald Trump, as well as members of his administration, have also expressed their displeasure with Pakistan on a number of fronts, including the fact that terrorist groups continuing to use Pakistani territory as a safe haven. In September 2018, the Trump Administration cut $300 million in aid to Pakistan over this particular issue.

"The United States has foolishly given Pakistan more than $33 billion in aid over the last 15 years, and they have given us nothing but lies & deceit, thinking of our leaders as fools," Trump had said in January 2018. "They give safe haven to the terrorists we hunt in Afghanistan, with little help. No more!"

If the United States ended support for the Vipers and blocked third parties from supplying parts and other services, it could ground what are objectively Pakistan's most capably combat aircraft in a very short amount of time. This could all help explain why the Pakistanis have been so keen to deny that their F-16s were even involved in their counter-strike on Indian positions Feb. 27, 2019, despite the high profile mission almost demanding their use.

It's also worth noting that as Pakistan has struggled to acquire new F-16s, Lockheed Martin has pitched advanced models to the Indian Air Force. The American defense contractor now looking to sell a rebranded advanced F-16 variant, dubbed the F-21, to India and potentially move significant portions of the Viper production line to the country. This could make it even more difficult for Pakistan to support the jets in the future.

Lockheed Martin

A rendering of the Lockheed Martin F-21, which the company says it would manufacture in India if it won a major contract.

It also remains to be seen just what impact the Indian insistence that F-16s were involved in the Feb. 27, 2019 aerial skirmish and that the Pakistanis lost one of these aircraft might have on efforts to de-escalate the present situation. Pakistan admitting it lost a combat jet publicly could prompt demands for renewed forceful action against India. Of course, it's hardly the first time the two countries have disputed significant and central details regarding major cross-border military skirmishes.

Pakistan's pledge to release Varthaman without any public concessions will be a significant act toward defusing tensions. India has also sent information on terrorist groups plotting attacks on Indian territory to the Pakistani government, which has promised to act on any credible information about these militant activities. Pakistan, however, has long denied that terrorists launch attacks on India from within its borders despite decades of well-established evidence to the contrary.

Whatever happens, the recovered piece of the AIM-120C-5 is strong evidence that Pakistani F-16s tangled with Indian jets for the first time in the air battle over Jammu and Kashmir.

Correction: The original version of this story said that Pakistan had only 45 F-16s. The actual total is approximately 76, with 45 of them being the AM/BM variants.